Ten genes show the way

Similar to the sugar glucose, its sulphurous analogue sulpho-glucose, is produced by all photosynthetically active organisms. The annual production of sulpho-glucose in nature is estimated at about ten billion tons. Researchers of the Department of Biology of the University of Konstanz, led by the microbiologists Dr. David Schleheck and Prof. Dr. Alasdair Cook, and supported by colleagues from the Department of Chemistry, have now revealed how sulpho-glucose is degraded. The scientists could identify one degradation pathway in the bacterium Escherichia coli, the most widely studied bacterial model organism: the sulpho-glycolytic pathway, encoded by ten genes, whose function had remained unknown thus far. The results have now been published in the online edition of Nature.

Sulpho-glucose is present in all plants, mosses, ferns and algae. The degradation pathway, or metabolic pathway, for sulpho-glucose, the sulpho-glycolysis, is therefore an important component of the material cycles in ecosystems.

As sulpho-glucose is not commercially available, Dr. Thomas Huhn of the neighbouring Department of Chemistry synthesised this special form of sugar in sufficient amounts and purity. The analytical-chemical studies to give proof of intermediates were conducted via modern mass spectrometry by the doctoral student Alexander Schneider and the chemists Prof. Dr. Christoph Mayer, now at the University of Tübingen, and Prof. Dr. Dieter Spiteller. "The excellent collaboration between biologists and chemists was an important aspect of our work. It also highlights the success of the research collaborations established between Biology and Chemistry within the framework of the Graduate Research School Chemical Biology at the University of Konstanz", says David Schleheck.

With their microbiological, molecular and biochemical work, the biologist Karin Denger and the doctoral students Michael Weiss and Ann-Katrin Felux were able to demonstrate that for sulpho-glycolysis, Escherichia coli does not use its already well-known enzymes for "normal" glycolysis. Instead, ten genes, whose function had remained completely unknown thus far, are responsible for the degradation of sulpho-glucose. Hence, the scientists closed another gap in the knowledge of the most widely studied model organism, Escherichia coli. Additionally, they discovered the new enzymes that catalyse sulpho-glycolysis.

It also became apparent that Escherichia coli cannot utilize sulpho-glucose completely, but excretes a sulphurous intermediate, which is degraded by other bacteria in the environment. "Therefore, we were able to demonstrate that sulpho-glucose is completely degraded in nature through the cooperation of several bacteria", explains Karin Denger.

The results of the microbiologists are not only relevant for botany, but also for human biology and zoology, since Escherichia coli is an important and valuable inhabitant of the human and animal intestinal tract, where plant nutrition also provides sulpho-glucose as a so far overlooked source of nutrients for this bacterium. The genes for sulpho-glycolysis are also present in pathogenic bacteria, such as in Salmonellae.

The project was supported by the Young Scholar Fund, established by the University of Konstanz within the German Excellence Initiative for supporting young researchers, by the Graduate Research School Chemical Biology, as well as by the German Research Foundation (DFG).

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